LONG HOLE DRILL WITH TITANIUM BASED CARBONITRIDE ALLOY INSERTS

Abstract: According to the invention there is now provided a drill head for long hole drilling provided with one or more cutting inserts. By using inserts of titanium based carbonitride alloy which are attached by brazing, followed by heat treating, or by using an adhesive, the cutting performance is improved.

Description: LONG HOLE DRILL WITH TITANIUM BASED CARBONITRIDE ALLOY INSERTS. The present invention relates to a long hole drill with improved performance. For drilling of holes with a depth greater than 10 times the diameter some type of long hole drilling meth¬ od has to be used. Long hole drills generally consist of a drilling head fastened to a shaft. The drilling head may be made of solid cemented carbide but is generally equipped with several cutting inserts of cemented car¬ bide located along the cutting edge. In the centre a tough grade is used while on the periphery a more wear resistant grade is used. The inserts are either brazed or mechanically fastened e.g. by clamping. In addition, the head is equipped with support pads also of cemented carbide. Normally, inserts of small diameter (65 mm or less) are brazed and larger diameters are clamped. The inserts and support pads are formed in accordance with known techniques of cemented carbide grades with various compositions of WC, Co and cubic carbides TiC, TaC, NbC etc depending on work material and application. Long hole drilling systems use high pressure of coo¬ lant as transportation media for the chips and to pre¬ vent the work piece material and inserts from obtaining too high a temperature. The cooling media are normally oils or emulsions . The cooling medium may be supplied through an internal channel and the chips removed exter¬ nally e.g. pipe-drilling. In the single tube system (STS) the cooling medium is supplied externally and the chips are removed internally. In the so called Ejector drill system the chips are removed through a centrally located inner tube with the cooling medium being provid¬ ed through a tube concentrically surrounding said inner tube. Fig 1 shows a typical drilling head Fig 2 shows a typical drilling head in top view. P - peripheral insert C - central insert M - intermediate insert S - support pads . Sintered titanium based carbonitride alloys, often referred to as cermets, are today well established as insert material in the metal cutting industry and are especially used for finishing. They contain mainly car¬ bonitride hard constituents embedded in a binder phase. The hard constituent grains generally have a complex structure with a core surrounded by a rim of other com¬ position. Their grain size is usually 1-2 μm. In addition to Ti, other metals of the groups IVa, Va and Via, i.e., Zr, Hf, V, Nb, Ta, Cr, Mo and/or W, are normally found in the carbonitride hard constituents but may also be present as carbide and/or nitride hard constituents . The binder phase generally contains cobalt as well as nickel. The amount of binder phase is gene¬ rally 3 - 30 % by weight. Titanium based carbonitride alloy are, however, known to be complicated to braze. The high thermal ex¬ pansion coefficient and low heat conductivity lead to built in tensile stresses which result in decreased toughness behaviour. The low K_ value (fracture tough¬ ness) for titanium based carbonitride alloy is also a disadvantage when tensile stresses are introduced during brazing. It has now surprisingly turned out that by providing the drill head with brazed peripheral cutting inserts of titanium based carbonitride alloy an unexpected improve¬ ment in performance, particularly when drilling in low carbon steel, can be obtained. The same grade can be used in both the central insert as well as in the one(s) located on the periphery. Particularly good results have been obtained with a titanium based carbonitride alloy of the composition: 15-25 % TiN, 20-30, preferably 24-26 % TiC, TaC+Mo 2 C+WC+VC+NbC 30-40 % and Co+Ni 15-17 %. Al- so an alloy with the composition 20-35, preferably 28- 35% TiN, 15-30 % TiC, TaC+Mθ2C+WC+VC+NbC 30-40 % and Co+Ni 15-17 % has shown promising results. Care is taken to eliminate or not to introduce stresses into the inserts. In order to be able to use titanium based carbonitride alloy in brazed drilling systems the following methods can be used. Brazing stresses can be relieved by a subsequent heat treatment. Alternatively, a soft braze with a melting point <450 °C can be used or the insert can be glued instead of brazed. Another alternative method is to grind reinfor¬ cement chamfers on the periphery of the inserts. Example 1 Drills according to the invention equipped with ti¬ tanium based carbonitride inserts with the following approximative composition in weight-% TiN 15, TiC 25, TaC 11, M02C 5, WC 18, NbC 2, Co+Ni 16 and commercially available drills, equipped with cemented carbide inserts were subjected to drilling test under the following con¬ ditions . Workpiece: 592 mm thick low carbon steel (SA 508) with an 8 mm thick Inconel 600 plate on top. Cutting data SA 508 InconelδOO v, m/min 92 40 f, mm/rev 0.17 0.1 Vf, mm/min 255 86 Drilling diameter: 19.4 mm Drilling depth: 600 mm Coolant: Oil Pressure: 60 bar Quantity: 140 1/min Criterion for tool change: Hole diameter min 19.36 mm. (Periphery insert) . Result Number of holes before Length, out of tolerance Prior art drill 12 7.2 According to the invention 26 15.6

Claims: Claims 1. Drill head for long hole drilling provided with one or more cutting inserts c h a r a c t e r i z e d in that at least the peripheral insert is made of titanium based carbonitride alloy. 2. Drill head according to the previous claim c h a r a c t e r i z e d in that all inserts have the same composition. 3. Drill head according to any of the previous claims c h a r a c t e r i z e d in that the inserts ha¬ ve the following composition: 15-25 % TiN, 20-30, pre¬ ferably 24-26 % TiC, TaC+Mo C+WC+VC+NbC 30-40 % and Co+Ni 15-17 %. 4. Drill head according to any of the previous claims c h a r a c t e r i z e d in that the inserts ha¬ ve the following composition: 20-35, preferably 28-35% TiN, 15-30 % TiC, TaC+Mθ2C+WC+VC+NbC 30-40 % and Co+Ni 15-17 % 5. Drill head according to any of the previous claims c h a r a c t e r i z e d in that the inserts ha¬ ve been brazed. 6. Drill head according to the previous claim c h a r a c t e r i z e d in that the inserts have been heat treated after the brazing. 7. Drill head according to claim 5 c h a r a c t e r i z e d in that the inserts have been brazed with a soft braze with a melting point <450°C. 8. Drill head according to any of the claims 1 to 4 c h a r a c t e r i z e d in that the inserts have been glued.

Inventors: BLOMBERG TORSTEN, WESTERGREN KENNETH, BLOMBERG, TORSTEN, WESTERGREN, KENNETH
Applicants: SANDVIK AB
Application year: 1994
Main classification: B23B27
IPC codes: B23B51